1. Field of the Invention
The present invention relates to a method of manufacturing a toner, and to a toner.
2. Description of the Related Art
An electrophotographic image forming apparatus comprises an image forming process mechanism including a photoreceptor; a charging section for charging a photoreceptor surface; an exposing section for irradiating with signal light the photoreceptor surface being charged, to form thereon an electrostatic latent image corresponding to image information; a developing section for supplying a toner contained in a developer to the electrostatic latent image formed on the photoreceptor surface, to form thereon a toner image; a transfer section provided with a transfer roller for transferring the toner image from the photoreceptor surface to a recording medium; a fixing section provided with a fixing roller for fixing the toner image onto the recording medium; and a cleaning section for cleaning the photoreceptor surface from which the toner image has been transferred. In the electrophotographic image forming apparatus, the electrostatic latent image is developed by use of a one-component developer containing a toner as a developer or by use of a two-component developer containing toner and carrier as developers so that an image is formed.
Through the electrophotographic image forming apparatus, an image of favorable image quality can be formed at high speed and low cost. This promotes the use of the electrophotographic image forming apparatus in a copier, a printer, a facsimile, or the like machine, resulting in a remarkable spread thereof in recent years. Simultaneously, the image forming apparatus has faced up to more demanding requirements. Among such requirements, particular attentions are directed to enhancement in definition and resolution, stabilization of image quality, and an increase in image forming speed, regarding an image being formed by the image forming apparatus. In order to fulfill these demands, a two-way approach is indispensable in view of both the image forming process and the developer.
Regarding the enhancement in definition and resolution of the image, the reduction in diameter of toner particles is one of problems to be solved from the aspect of the developer. This is based on the perspective such that it is important to authentically reproduce the electrostatic latent image. Typically, the toner particles are resin particles formed of wax which serves as a colorant or releasing agent, dispersed in binder resin serving as a matrix. It is thus difficult to reduce the diameter of the wax dispersed in the binder resin by a commonly-used method of manufacturing diameter-reduced toner particles. In this case, a problem arises such that the diameter-reduced toner particle thus manufactured has its wax bleeding out over time, thus causing toner filming on a photoreceptor. In addition, a large amount of wax bleeds out onto a surface of the toner particle, and particularly when the temperature is high, the wax is fused and thus exhibits viscosity. Consequently, this makes it extremely easy to cause an offset phenomenon that the toner is not transferred or fixed onto a recording medium but attached to a transfer roller, a fixing roller, or the like component.
As a method of reducing the diameter of the wax, a toner manufacturing method including a mixing step, a melt-kneading step, and a pulverizing-classifying step has been proposed, for example (refer to Japanese Unexamined Patent Publication JP-A 6-161153 (1994), for example). In this method, at least 100 parts by weight of thermoplastic resin and 1 to 7 parts by weight of wax are mixed at the mixing step. The melt-kneading step is a step for melting and kneading the admixture obtained at the mixing step, where a melt-kneading temperature falls in a range of from (Tm−20)° C. to (Tm+20)° C. wherein Tm represents a melting temperature of the thermoplastic resin, and a temperature of melt-kneaded product after the melt-kneading process is (Tm+35)° C. or less. Further at the pulverizing-classifying step, the melt-kneaded product-obtained at the melt-kneading step is cooled down to be then pulverized and classified.
Further, there has been proposed a toner manufacturing method composed of melt-kneading an admixture of toner raw material, and cooling down, pulverizing and classifying the obtained melt-kneaded product, the toner manufacturing method in which the admixture of toner raw material is melt-kneaded by using a kneading extruder configured such that a slide-shaped discharging portion inclining downward is coupled on an outlet of a cylinder portion having a kneading-conveying member therein for kneading and conveying the admixture of toner raw material (refer to Japanese Unexamined Patent Publication 9-277348 (1997)).
In the above manufacturing methods, the diameter of the wax contained in the toner particles is reduced whereby the toner filming on the photoreceptor caused by bleeding out of the wax and the offset phenomenon are aimed to be prevented. These methods which are basically the heretofore known melt-kneading methods may succeed in reducing the diameter of the wax, but fail to contribute to sufficient reduction of the toner particle itself. Accordingly, the toner particles obtained through these methods are not fully satisfactory in terms of the image reproducibility including definition and resolution in particular.
Meanwhile, there has been proposed an emulsifying/dispersing apparatus comprising: an emulsifying/dispersing section for emulsifying/dispersing by a shearing force an emulsifying material in a liquid serving as a matrix; a leading passage for supplying a multistage depressurization section with the pressurized emulsified liquid obtained by the emulsifying/dispersing section; a heat exchanging section disposed on the leading passage; and a multistage depressurization section for allowing the emulsified liquid supplied from the leading passage to have a reduced pressure causing no bubbling even if it is released to atmosphere, and then discharging the emulsified liquid (refer to International Publication WO03/059497, for example). In the emulsifying/dispersing apparatus, the emulsifying material is dispersed in a liquid under pressure, thereby preparing the emulsified liquid in which the emulsifying material is evenly dispersed. Next, the pressure on the emulsified liquid is reduced in a stepwise manner so that the final pressure is at a level causing no bubbling. By so doing, particles of the emulsifying material dispersed in the emulsified liquid are prevented from coarsening. The emulsifying/dispersing apparatus thus aims to obtain an emulsified liquid in which particles of emulsifying material having a uniform particle diameter are dispersed. By use of this emulsifying/dispersing apparatus which has the multistage depressurization section, a large shearing force can be given by the emulsifying/dispersing section, so that an emulsion of water/oil, for example, can be easily manufactured. However, on attempts to obtain toner particles by use of this apparatus only, it is difficult to control the particle diameter, so that desired toner particles with a reduced diameter cannot be obtained. Further, WO03/059497 has no disclosure about application of this emulsifying/dispersing apparatus to a manufacture of toner particles. Furthermore, WO03/059497 has no suggestion about the effect that the use of this emulsifying/dispersing apparatus in manufacturing the toner particles makes it possible to obtain a toner in which not only a diameter of toner particle is reduced but also wax contained in the toner particles, having more reduced diameter than that of the toner particle is evenly dispersed.